If is often desirable to measure physical data, such as temperature, pressure and fluid velocity and/or composition in a fluid transportation conduit. However, it is not always feasible or economically attractive to provide the conduit with sensors which are able to measure such data along the length of the conduit over a prolonged period of time. In such circumstances so called intelligent pigs have been used to measure data, but since these pigs are pumped through the conduit they are large pieces of equipment which span the width of the conduit and therefore are not suitable to make in-situ measurements in the fluid flowing through the conduit. Also tethered sensor probes have been used to measure data in conduits, but these probes have a limited reach and involve complex and expensive reeling operations.
International patent application PCT/US97/17010 discloses an elongate autonomous robot which is released downhole in an oil and/or gas production well by means of a launching module that is connected to a power and control unit at the surface. The elongated robot is equipped with sensors and arms and/or wheels which allow the robot to walk, roll or crawl up and down through a lower region of the well. The insertion of the launching module into the well and the movement of the robot through the well is a complex operation and requires complex, fragile and expensive propulsion equipment.
U.S. Pat. No. Re. 32,336 discloses an elongate well logging instrument which is lowered into a borehole at the lower end of a drill pipe. When the pipe has reached a lower region of the borehole the logging tool is released, lowered to the bottom of a well and retrieved by means of an umbilical that extends through the drill pipe towards the wellhead.
U.S. Pat. No. 3,086,167 discloses a borehole logging tool which is dropped through a drill string to a location just above the drill bit to take measurements during drilling. The tool can be retrieved from the drill string by means of a fishing tool.
U.S. Pat. Nos. 4,560,437 and 5,553,677 and International patent application WO 93/18277 disclose other elongate downhole sensor assemblies that are removed from the well by means of a fishing tool or an umbilical.
It is an object of the present invention to provide a method and system for measuring data in a fluid transportation conduit over a prolonged period of time and which do not require permanently installed sensors, complex wireline tools and/or robotic transportation tools and which employ a sensing device which can be moved through the conduit without obstructing the conduit so that it is able to make in-situ measurements in the fluid within the conduit.